1. Field of the Invention
The present invention relates to an electrodeless discharge lamp.
2. Prior Art
An electrodeless discharge lamp generates visible light, UV light, or the like by exciting light-emitting gases such as an inert gas, mercury, and metal halide with an electromagnetic wave generated from a coil. Because of the electrodeless structure, the electrodeless discharge lamp is unlikely to degrade, resulting in a long life. Thus, in recent years since resource-saving has been sought, there is an increasing demand for development of the electrodeless discharge lamp.
FIG. 12 is a cross-sectional view of a main portion (light-transparent envelope) having a structure of a conventional electrodeless discharge lamp disclosed in Japanese laid open Publication No. 10-112293. Reference numeral 1201 denotes a base for supplying alternating current (AC) power. Reference numeral 1202 denotes a power source circuit which generates a sine wave and is connected to the base 1201 and a coil 1203. A magnetic material such as ferrite is disposed in the coil 1203. It is considered that the magnetic material is linear and positioned so as to be perpendicular to the axis of the lamp passing through the center of the base.
In the above-mentioned structure, an end portion of the magnetic material of the coil is not directed toward the base. Therefore, there are advantages in that the possibility of interference between the magnetic field and a metal portion of the lighting equipment in relatively small, and an operation point is not likely to be moved by changes in inductance, etc.
However, in the electrodeless discharge lamp with the above-mentioned structure, a half or more of the magnetic field generated by the coil leaks outside from the light-transparent envelope, as represented by a magnetic field xcex4 in FIG. 12. Therefore, magnetic flux which is generated inside the light-transparent envelope and contributes to light emission of the lamp is reduced to a half or less of the entire magnetic flux, which decreases the light emission efficiency of the lamp.
Furthermore, the magnetic field which leaks in the direction of the base interferes with lighting equipment, which changes inductance and moves an operation point to decrease the light emission efficiency of the lamp.
Furthermore, the density of the magnetic flux in the envelope is not uniform and brightness in the light-transparent envelope becomes non-uniform depending upon the position during light emission, which degrades the quality of the lamp.
The present invention solves the above-mentioned problems. More specifically, the objective of the present invention is to improve a light emission efficiency of the lamp by suppressing magnetic flux which leaks outside the light-transparent envelope, thereby preventing interference between the magnetic flux and the metal portion of lighting equipment and increasing the density of magnetic flux generated inside the light-transparent envelope.
In order to achieve the above-mentioned objective, the electrodeless discharge lamp of the present invention is composed of a light-transparent envelope in which light-emitting materials such as an inert gas, mercury and metal halide are sealed and a coil having a magnetic material which applies an electromagnetic field to the light-transparent envelope. In at least one structure of the coil, at least one end portion of the magnetic material is disposed substantially parallel to the axis of the light-transparent envelope.
Furthermore, the present invention is characterized in that the end portions of the magnetic material have the maximum density of magnetic flux.
Furthermore, the present invention is characterized in that both ends of the magnetic material are substantially parallel to the axis of the light-transparent envelope.
Furthermore, the present invention is characterized in that the magnetic material has three or more end portions, and a part or an entirety of the end portions are disposed substantially parallel to the axis of the light-transparent envelope.
Furthermore, the present invention is characterized in that a part or all of the magnetic material is a material magnetized in a particular direction.
Furthermore, the present invention is characterized in that the coil reaches the vicinity of the end portions of the magnetic material.
Furthermore, the present invention is characterized in that the end portions of the magnetic material are edge portions substantially in the shape of a circle or of a polygon, and end portions of the magnetic material having an opposite polarity of that of the edge portions are preset in the edge portions.
Furthermore, the present invention is characterized in that a power source circuit for supplying high-frequency electric power to the coil is built in the lamp.